CVE-2026-55040

Microsoft SharePoint Server Security Feature Bypass Vulnerability

CVE-2026-55040 is fixed in 3 products on 1 platform, first by KB5002891, released July 14, 2026. It is being exploited: CISA added it to the Known Exploited Vulnerabilities catalog on August 18, 2026. Patch Radar priority: Patch now.

Patch nowCISA KEV

CVSS

9.1

Critical

Exploitation

Exploited

Listed by CISA

CISA KEV

Aug 18, 2026

Federal due date Aug 21, 2026

EPSS

0.6954

99th percentile

<p>Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.</p>

Where it's fixed

Product	Fix	Released
Microsoft
Microsoft SharePoint Enterprise Server 2016	KB5002891	Jul 14, 2026
Microsoft SharePoint Server 2019	KB5002883	Jul 14, 2026
Microsoft SharePoint Server Subscription Edition	KB5002882	Jul 14, 2026

Details

Published
July 14, 2026
Weakness
Weak Authentication
CISA required action
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040

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